docs: def display_system(sys, style='vdw'):
      '''Display the system *sys* with the default viewer.
  
      '''
      
      v = QtViewer()
  
      #v.add_post_processing(FXAAEffect)
      v.add_post_processing(SSAOEffect)    
      
      if style == 'vdw':
          sr = v.add_renderer(AtomRenderer, sys.r_array, sys.type_array,
                              backend='impostors')
      if style == 'ball-and-stick':
          sr = v.add_renderer(BallAndStickRenderer,
                              sys.r_array,
                              sys.type_array,
                              sys.bonds)
      
      if sys.box_vectors is not None:
          v.add_renderer(BoxRenderer, sys.box_vectors)
          
          # We autozoom on the box
          a, b, c = sys.box_vectors
          box_vertices = np.array([[0.0, 0.0, 0.0],
                                   a, b, c,
                                   a + b, a + c, b + c,
                                   a + b + c])
          v.widget.camera.autozoom(box_vertices)
      else:
          v.widget.camera.autozoom(sys.r_array)
      
      v.run()